                                             while (i < j) {
         /**
          * Definition for singly-linked list.
           * struct ListNode {
                *     int val;
                 *     ListNode *next;
                  *     ListNode() : val(0), next(nullptr) {}
                   *     ListNode(int x) : val(x), next(nullptr) {}
                    *     ListNode(int x, ListNode *next) : val(x), next(next) {}
                     * };
                      */
                      class Solution {
                          public:
                              bool isPalindrome(ListNode* head) {
                                          string s;
                                                  ListNode* cur = head;
                                                          while (cur) {
                                                                          char c = '0' + cur->val;
                                                                                      s += c;
                                                                                                  cur = cur->next;
                                                          }
                                                                  int i = 0, j = s.size() - 1;
                                                                          while (i < j) {
                                                                                          if (s[i] == s[j]) {
                                                                                                              ++i;
                                                                                                                              --j;
                                                                                          } else {
                                                                                                              return false;
                                                                                          }
                                                                          }
                                                                                  return true;
                              }
                      };
                                                                                          }
                                                                                          }
                                                                          }
                                                          }
                              }
                      }
           }                                                                        if (s[i] == s[j]) {
                                                                                                     ++i;
                                                                                                                     --j;
                                                                                 } else {
                                                                                                     return false;
                                                                                 }
                                                                 }
                                                                         return true;
                     }
             };:
                                                                                 }
                                                                                 }
                                                                 }
                                                 }
                     }
             }
  }